Zinc oxide (ZnO) nanoparticle-based nanocomposite polymer electrolytes with a very high luminescence intensity were prepared by an in situ method, in which ZnO nanoparticle fillers were grown in the polymer matrix and ion carriers were inserted during the growth of the nanoparticles (contributed by a precursor). By using a high concentration of lithium hydroxide (LiOH) as the precursor, the remaining unreacted LiOH was distributed in the form of an amorphous complex around the produced ZnO nanoparticles, thus preventing the agglomeration of the nanoparticles. This resulted in a high number concentration of ZnO nanoparticles that serve as luminescent centers for inducing a high luminescence intensity. Compared to samples prepared using the usual concentration of LiOH (about 0.14 M), the luminescence intensity was enhanced by about 22 times for the ZnO nanopowder and 6 times for the nanocomposite polymer electrolytes (poly(ethylene glycol)/ ZnO/Li+) when a LiOH concentration of 0.35 M was used.